Announce changed emoji

[davedelong]

It'd be cool if Camille could announce the creation of new emoji: https://api.slack.com/events/emoji_changed

You might want to do some sort of coalescing in case an emoji is being edited (like, wait a couple of minutes just in case someone is doing a delete + add to fix a transparency issue or something), but listening for an emoji_changed event should be pretty straight-forward.

From there, it'd be a matter of posting in the proper channel that:

Rejoice! @some_user has created the :whatever: emoji! :whatever: